Maintenance of Remission and Risk of Relapse in Myeloperoxidase-Positive ANCA-Associated Vasculitis with Kidney Involvement

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records and included demographic characteristics, comorbidities, laboratory findings, biopsy results, therapies, and outcomes.The date of kidney involvement diagnosis (reference date) was registered to calculate outcomes time-points.The Birmingham Vasculitis Activity Score for Wegener´s Granulomatosis (BVAS/WG) was used to quantify disease severity at presentation and during followup. 2O-ANCA positive patients with newly diagnosed AAV or relapsing disease with active kidney involvement and fulfilling the American College of Rheumatology (ACR) criteria and Chapel Hill consensus definition for granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA) were included (Fig. 1). 3,4The clinicopathologic diagnosis originally assigned by the clinician was accepted.A known remission status, a defined remission-maintenance strategy and a minimum of 6 months of follow up after achieving remission was required for inclusion.Outcome assessment.Remission was defined by a BVAS/WG of 0 independent of the prednisone dose, and sustained remission was defined by a BVAS/WG of 0 present for more than 6 months independently of the prednisone dose.These events were assessed at 6 months and during follow-up.All patients included in the analysis achieved remission.Relapse was defined by an increase of BVAS/WG > 1 after remission had been achieved, that resulted in therapy changes (increases in doses of remission-maintenance therapy or the start of a new remission-induction cycle).
Time to relapse after remission (independently of ANCA-status at the time of remission); the number of relapses after the achievement of remission; type of relapse (major [BVAS/WG>3] or minor); the organ involvement (renal versus non-renal); and the BVAS/WG at the time of relapse were recorded.

Immunosuppression withdrawal and relation with relapse.
We classified the patients into 4 groups: (i) patients who were withdrawn from therapy and did not relapse; (ii) patients who were withdrawn from therapy and relapsed; (iii) patients who were not withdrawn from therapy and did not relapse; (iv) patients who were not withdrawn from therapy and relapsed.

Statistical analysis.
Categorical variables were presented as count (percent), while continuous variables were presented as mean (standard deviation) if they were normally distributed as determined by the Shapiro-Wilk test or as median (interquartile range [IQR]) if not normally distributed.Pearson's chi-square test was used to compare categorical variables between groups.The Bonferroni correction for multiple comparisons was applied when more than two categories of categorical variables were compared.For comparison of continuous variables between two groups, an unpaired Student's t-test for independent samples was used for distributions consistent with normality, and the Mann-Whitney U test was used otherwise; for comparison of continuous variables between more than two groups, an ANOVA test was used for distributions consistent with normality, and the Kruskal-Wallis test was used otherwise.There was no imputation or removal of data due to missing data since the variables of interest were complete for all the patients.
16. Hernan MA: The hazards of hazard ratios.Epidemiology.2010 Logistic regression models were developed to examine the predictive role of the baseline clinical organ involvement and remission-induction treatment impact on therapy withdrawal.
Variables were considered for the multivariable logistic regression models if they occurred before the development of the outcome of interest, had <10% of missing values, had p values < 0.05 in the univariate analysis, and were clinically plausible.The final model was determined using both clinical and statistical criteria, considering collinearity, interaction, and the number of patients who experienced the outcome of interest.The odds ratios (OR) with a 95% confidence interval (95% CI) were reported when appropriate.
The Kaplan Meier method was used to assess the cumulative incidence of relapse after achieving remission.Cox proportional hazards regression models were used to determine predictive factors for relapse at 60 months.We report the HR with a 95% CI when appropriate. 16The final model was determined using both clinical and statistical criteria, considering collinearity, interaction, and the number of patients who experienced the outcome of interest.We evaluated the following covariates: age at diagnosis, gender, new diagnosis vs. previous relapse, type of AAV (MPA vs. GPA), BVAS/WG score, type of organ involvement on the BVAS/WG score, alveolar hemorrhage, arterial hypertension, diabetes mellitus, dyslipidemia, BMI > 30 kg/m2, hemoglobin, eGFR at diagnosis, eGFR at diagnosis < 30 mL/min/1.73m2,eGFR at diagnosis < 15 mL/min/1.73m2,remission-induction therapies, remission-induction adjuvant therapies, type of remissionmaintenance therapies, ANCA status.and keeping or stopping immunosuppression.The final model included only variables that were statistically significant in the univariable analysis (p<0.05) or that are known to be associated with higher risk of relapse (for instance, ear nose and throat involvement).
We performed backward method for selection of the model.The frequency of death prior to 60 months was ≤10%, and therefore, the risk of being a competitive event over such a long period of time was considered negligible.
MPO-ANCA status classification and serial determinations.Patients were longitudinally analyzed and classified into 3 categories according to their MPO-ANCA status at the end of the follow-up: (i) sustained seronegative: patients that turned MPO-ANCA negative at any time during follow-up and remained negative; (ii) reappearance: patients that turned MPO-ANCA positive after becoming MPO-ANCA negative; and (iii) persistently positive, patients who remained MPO-ANCA positive throughout the entire follow-up period.The MPO-ANCA status at the time of remission (BVAS/WG = 0) was also recorded.MPO-ANCA serial determinations at all available time points were recorded.ANCA specificity was determined by solid-phase immunoassays and complemented by indirect immunofluorescence characterization of a perinuclear pattern (p-ANCA).15Serial MPO-ANCA determinations were recorded at all available time points.MPO-ANCAspecificity was determined by solid phase immunoassays and complemented by indirect immunofluorescence (IIF) characterization of a perinuclear pattern (p-ANCA).Over time, 4 assays were used to determine MPO-ANCA, and we analyzed each patient's results and status along time with the assay used in mind: a) On 10/16/1991, the lab implemented the first anti-MPO assay (BioCarb Diagnostics distributed by Scimedx Corp).For this assay, <10 U is normal.b) On 2/20/2003, the lab changed methods to Scanlisa MPO Antibody assay from SciMedx Corp.The cut-offs for this assay are: Negative </= 5.0 U/mL, Equivocal 5.1-14.9U/mL, and Positive >/= 15.0 U/mL.c) On 9/19/2006, the lab changed methods again to Varelisa MPO kit (Pharmacia Diagnostics.The cut-offs for this assay are: Negative < 6.0 U/mL, Equivocal 610/2008, the lab changed to our current method (BioPlex by BioRad).The cutoffs for the current assay are: Negative < 0.4 U, Equivocal 0.4-0.9U, and Positive >/= 1.0 U/mL When borderline or equivocal by MPO-specific immunoassay, the status was determined by combining the MPO-ANCA serology with IIF results: if both positivepositive; if equivocal result by MPO-specific immunoassay and IIF negativenegative; if equivocal by MPO-specific immunoassay and positive on IIF-positive.
13.Charles P et al.Comparison of individually tailored versus fixed-schedule rituximab regimen to maintain ANCAassociated vasculitis remission: results of a multicentre, randomised controlled, phase III trial (MAINRITSAN2).Ann Rheum Dis.2018. 14.Smith RM.Rituximab as therapy to induce remission after relapse in ANCA-associated vasculitis.Ann Rheum Dis.2020.
5. Levey AS et al.Nomenclature for kidney function and disease: report of a Kidney Disease: Improving Global Outcomes (KDIGO) Consensus Conference. 13.Charles P et al.Comparison of individually tailored versus fixed-schedule rituximab regimen to maintain ANCAassociated vasculitis remission: results of a multicentre, randomised controlled, phase III trial (MAINRITSAN2).Ann Rheum Dis.2018. 14.Smith RM.Rituximab as therapy to induce remission after relapse in ANCA-associated vasculitis.Ann Rheum Dis. 15.Russell KA et al.Detection of anti-neutrophil cytoplasmic antibodies under actual clinical testing conditions.Clin Immunol.2002

Table 3 -
Comparison of treatment and outcomes of patients according with the period of time of AAV-GN diagnosis.IQR -interquartile range; IVintravenous; n-number.